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An approach for evaluating the significance of potential fault sources on seismic hazard: A case study using the August 2011
Mineral, Virginia, aftershock-delineated fault source
Lisa Schleicher and Clifford MunsonU.S. Nuclear Regulatory Commission, Office of New Reactors
Division of Site Safety and Environmental Analysis(Contact Information: [email protected], 301-415-5612)
2016 Natural Phenomena Hazards Meeting and Training Session, October 19, 2016
Introduction
• When does new information trigger need to update the CEUS-SSC (or other) seismic source models?
• Need for traceable methods, vs. expert judgement, for model updates
• Approach: Evaluate new information from the aftershock-delineated fault source from the August 2011 Mineral, VA, earthquake (termed the Quail fault) and determine if it affects the PSHA and use of the CEUS-SSC model?
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Presentation Outline
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3) Quail Postulated
Fault Source
Initial analysis and
discussion
2) Example
New Madrid
Fault Source
(NMFS)
1) Methodology
Approach to
quantitatively evaluate
potential significance of
new information to
PSHA within CEUS-
SSC framework
Methodology: Performing a Sensitivity Analysis by adding a Postulated Fault Source to the CEUS-SSC
1. Determine hazard at site using CEUS-SSC and EPRI GMM
2. Compare the rates from the CEUS-SSC background seismicity sources with the postulated recurrence rates for the postulated fault source
3. Determine hazard at site from the postulated fault source
4. Compare the hazard at site with and without adding the postulated fault source at 10-4 and 10-5 annual frequencies of exceedance
5. Make final evaluation as to whether adding the postulated fault source significantly impacts the hazard at site
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Postulated RLME Example : NMFS
• Assume NMFS has not been included as an RLME in CEUS-SSC model
• Does adding NMFS RLME significantly impact the 1 Hz hazard at Toledo, OH?
CEUS-SSC Mmax Zones & RLMEs w/in 500 km
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Earthquakes ≥ magnitude2.0 – red, 3.0 – green, 4.0 – blue,
5.0 – orange, 6.0 – purple, 7.0 – black
320 km
500 km
NMN
RFT
NMS
Postulated RLME: NMFSNMN: New Madrid NorthNMS: New Madrid SouthRFT: Reelfoot Thrust
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Earthquakes ≥ magnitude2.0 – red
3.0 – green4.0 – blue
5.0 – orange6.0 – purple7.0 – black
Overall CEUS-SSC Seismic Source Logic Tree
Conceptual Approach Source Groups
Mmax Zones
SeismotectonicZones
SeismotectonicZones
RLME
RLME
Mmax Zones
(0.4)
(0.6)
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Seismotectonic Zones: RR and RR-RCG
Mmax Zones: MESE-N, MESE-W, Study-R
RRMESE-N
0.25 spacing: 32 grid cells 0.50 spacing: 8 grid cells
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8 realizations x 3 cases (case A, B, E)
= 24 rates for each source
Earthquakes ≥ magnitude2.0 – red, 3.0 – green, 4.0 – blue,
5.0 – orange, 6.0 – purple, 7.0 – black
Recurrence rates forpostulated NMFS RLME
Background Zone grid cells encompassing NMFS
Does Rate from Background Zones Capture Postulated RLME Rates for NMFS?
Mean Return Periods (yr): 167417
1613
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TotalMIDC-ANMESE-NSTUDY_RMIDC-BIBEBMIDC-CNMESE-WMIDC-DPEZ-NPEZ-WWabash
Dashed Lines NMFS: Mean Recurrence Period (MRP) (yr)1674171613
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CEUS-SSC baseline hazard
+Hazard for the
NMFS Postulated RLME for varying recurrence rates
TotalMIDC-ANMESE-NSTUDY_RMIDC-BIBEBMIDC-CNMESE-WMIDC-DPEZ-NPEZ-WWabash
Dashed LineTotal + NMFS: MRP 417 yr
• Due to large source-to-site distance adding NMFS RLME (MRP: 417yr) increases the 1 Hz SA by a fairly small amount at Toledo, OH
• 10-4 AEF: 0.03 g to 0.04 g
• 10-5 AEF: 0.08 g to 0.10 g
• Sensitivity study assesses impact of postulated RLME on 1 Hz hazard for site, but study does not evaluate plausibility of postulated RLME
Conclusion – Postulated NMFS
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Background Information –Quail Fault
A multi-institution deployment of seismometers in the epicentral region yielded a well-recorded (>395 events) aftershock sequence for the Mineral earthquake
Aftershock-delineated fault plane – termed the “Quail Fault” (Horton et al., 2015, doi:10.1130/2015.2509(14)):
• N36°E, 50°SE
• Length = ~10 km
• Width = ~8 km
• Depth = 7 km
Figure 4B from Walsh et al., 2015, doi:10.1130/2015.2509(18) 12
Area Sources: Mmax Zones
320 km
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Earthquakes ≥ magnitude2.0 – red
3.0 – green4.0 – blue
5.0 – orange
NMESE-N
MESE-N
Area Sources: Seismotectonic Zones
MIDC-A
PEZ-NECC-AM
AHEX
320 km
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Earthquakes ≥ magnitude2.0 – red
3.0 – green4.0 – blue
5.0 – orange
Test Site 18: 5 km southeast of
epicenter (hanging wall of Quail fault)
TotalAHEXECC_AMMESE-NMIDC-AMIDC-BMESE-WNMESE-NPEZ-NPEZ-WSTUDY_R
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CEUS-SSC baseline hazard
Seismotectonic Zones: ECC_AM Mmax Zones: MESE-N, MESE-W, Study-R
0.25 spacing: 16 grid cells 0.50 spacing: 8 grid cells
PEZ-N
ECC-AMMESE-N
NMESE-N
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Quail Postulated Fault Source
• Grid spacing is same as NMFS
• Source only resides in 2 grid cells (beneath triangle marking center of fault)
• Expand to capture background seismicity rate in nearby central Virginia seismic zone
Earthquakes ≥ magnitude2.0 – red
3.0 – green4.0 – blue
5.0 – orange
CEUS-SSC Model includes 24 rates (defined by a and b-values) for each source 8 realizations of recurrence maps x 3 cases (case A, B, E)
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Realization 1 Realization 2 Realization 3 Realization 4
Realization 5 Realization 6 Realization 7 Realization 8
From NUREG-2115 (CEUS-SSC Model) – Appendix J
Next Steps – Postulated Quail Fault RLME
• Extract seismicity rates for mmax and seismotectonic grid cells and create magnitude – rate plot for establishing recurrence characterized by background sources
• Run hazard for the Quail Postulated Fault Source using faultsource_31program together with EPRI (2013) GMMs for a range of recurrence rates (0.01, 0.1, 1, and 10 mm/yr)
• Compare the hazard at site with and without adding the postulated fault source at 10-4 and 10-5 annual frequencies of exceedance for 25 test sites (0, 5, 25, 50 km from postulated fault)
• Make final evaluation as to whether including the Quail Postulated Fault Source in CEUS-SSC significantly impacts the hazard at the test sites
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Preliminary Conclusions
• This sensitivity study provides a traceable approach for quantifying and visualizing the potential significance of an aftershock-delineated rupture plane on an existing PSHA in central Virginia
• Geologic and seismic field evidence of recurrence seismicity of the Quail Fault would need to be established before including the aftershock-delineated rupture plane as a discrete seismic source in the CEUS-SSC model
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